If the efficiency of communication in a parallel computer is increased by optimization of a coupling mode (for example, network topology) of a server and a switch in the parallel computer, the throughput of parallel distributed processing executed by the parallel computer may be improved. Further, if a great number of servers may be coupled by a small number of switches by optimization of the network topology in a parallel computer, the construction cost of the parallel computer may be suppressed.
A network topology called Latin square fat-tree is known. The Latin square fat-tree has a characteristic that only one route through a Spine switch exists between two arbitrary different Leaf switches. If the Latin square fat-tree is used, a great number of servers may be coupled by a same number of switches in comparison with a two-stage fat-tree.
In a parallel computer, collective communication called Allreduce communication is executed. The Allreduce communication is communication in which a result of arithmetic operation executed using data all target nodes have is shared by all target nodes, and Allreduce signifies the arithmetic operation. If Allreduce by all servers of a system that adopts the Latin square fat-tree (the system is hereinafter referred to as Latin square fat-tree system) may be implemented, parallel distributed processing that uses a greater number of servers may be executed.
Related techniques are disclosed in, for example, M. Valerio, L. E. Moser and P. M. Melliar-Smith, “Recursively Scalable Fat-Trees as Interconnection Networks,” IEEE 13th Annual International Phoenix Conference on Computers and Communications, 1994.